The present invention relates to NiMnZn based ferrite applicable to cores for transformers and choke coils to be used in broad temperature ranges, and transformers and choke coils employing the same.
Mnxe2x80x94Zn based ferrite, comparing with other ferrite materials and soft magnetic metal materials, is small in an power loss, and is relatively large in a saturation magnetic flux density, when it is used as a core for a transformer for switching power supply to be used in frequency ranges of several tens kHz to several hundreds kHz. Accordingly it has been an important material as cores for transformers and choke coils.
However, recently, with miniaturization of electronic machines and making high power output, demands have been increased for using under conditions at high temperatures in using circumstances as parts of vehicles (at least 100xc2x0 C., preferably 150xc2x0 C.), and conventional ferrite materials are insufficient in the saturation magnetic flux density Bs, in particular the saturation magnetic flux density Bs in ranges at high temperature.
JP-B-63-59241 and JP-B-63-59242 disclose the ferrite materials where at least one of Ni, Mg and Li ferrites is substituted for parts of Mnxe2x80x94Zn based ferrite to be a low power loss under using circumstances at 150xc2x0 C. or higher and high magnetic stability, but the saturation magnetic flux density Bs characteristic at high temperature is insufficient.
JP-A-2-83218 discloses NiMnZn based ferrite where the stability of magnetic characteristic is high at high temperature and under high magnetic field, the saturation magnetic flux density Bs is high and power loss is low. But the saturation magnetic flux density Bs characteristic at high temperature is insufficient.
The above mentioned conventional ferrite materials are involved with the following problems.
(1) : When ferrite materials are to be used for transformers and choke coils, in general designs are planned with respect to characteristics under possibly highest temperature condition, but any of the above conventional examples is insufficient in the saturation magnetic flux density Bs at high temperature ranges.
(2): When ferrite materials are to be used for transformers and choke coils, if the saturation magnetic flux density Bs is high and coercivity Hc is small in the relation between the saturation magnetic flux density Bs and the coercivity Hc, an initial magnetization curve of B-H loop steeply stands until a magnetic flux near a saturated condition, and as a result, DC pre-magnetization is desirable (even if DC is overlapped in the vicinity of the saturation magnetic flux density, an inductance L is not decreased), but in materials of the large coercivity Hc, the initial magnetization curve of B-H loop steeply stands at the first half thereof but at the middle, it becomes moderately oblique, and in the vicinity of the magnetic flux near the saturated condition it draws a very small slope. Therefore, if the DC pre-magnetization is evaluated, the inductance decreases before the saturation of the magnetic flux, and in spite of the high Bs characteristic, its characteristic cannot be demonstrated, and as a result, a desirable DC pre-magnetization is not available.
With respect to the saturation magnetic flux density Bs and the coercivity Hc of all of the above mentioned conventional examples, such characteristics cannot be obtained that the saturation magnetic flux density Bs is high and the coercivity Hc is small, and the desirable DC pre-magnetization is not available.
It is accordingly an object of the invention to provide NiMnZn based ferrite which is excellent in the DC pre-magnetization and low in power loss from a room temperature to around 150xc2x0 C.
According to first aspect of the invention, NiMnZn based ferrite comprising: main components comprising iron oxide 53 to 59 mol % in term of Fe2O3, manganese oxide 22 to 41 mol % in trem of MnO, zinc oxide 4 to 12 mol % in term of ZnO, and nickel oxide 2 to 7 mol % in term of NiO; and sub-components comprising silicon oxide 0.005 to 0.03 wt % in term of SiO2, calcium oxide 0.008 to 0.17 wt % in term of CaO and phosphorus P 0.0004 to 0.01 wt %.
According to second aspect of the invention, NiMnZn based ferrite, main components comprising iron oxide 53 to 59 mol % in term of Fe2O3, manganese oxide 22 to 39 mol % in trem of MnO, zinc oxide 4 to 12 mol % in term of ZnO, and nickel oxide 4 to 7 mol % in term of NiO; and sub-components comprising silicon oxide 0.005 to 0.03 wt % in term of SiO2, calcium oxide 0.008 to 0.17 wt % in term of CaO and phosphorus P 0.0004 to 0.01 wt %.
In NiMnZn based ferrite as set forth in the above, at least one the following additives are added in predetermined ranges of Nb2O5: 0.005 to 0.03 wt %, Ta2O5: 0.01 to 0.08 wt %, V2O5: 0.01 to 0.1 wt %, ZrO2: 0.005 to 0.03 wt %, Bi2O3: 0.005 to 0.04 wt % and MoO3: 0.005 to 0.04 wt %.
In NiMnZn based ferrite as set forth in the above, an average grain size a sintered body is 6 to 25 xcexcm.
In NiMnZn based ferrite as set forth in the above, the saturation magnetic flux density Bs (100xc2x0 C.) of a sintered body is 440 mT or more.
In NiMnZn based ferrite as set forth in the above, the relation between the saturation magnetic flux density Bs (150xc2x0 C.) and the coercivity HC (150xc2x0 C.) of the B-H loop satisfies the condition of R=(Bsxe2x88x92300)2/Hc, (herein Rxe2x89xa7400).
For a transformer or a choke coil, NiMnZn based ferrite as set forth in any of the above is used.
By such structures as mentioned above, the following performance is exhibited.
In NiMnZn based ferrite, the main components range within the scopes of Fe2O3=53 to 59 mol %, MnO=22 to 41 mol %, ZnO=4 to 12 mol %, and NiO=2 to 7 mol %, and the sub-components of said NiMnZn based ferrite range within the scopes of SiO2: 0.005 to 0.03 wt %, CaO: 0.008 to 0.17 wt % and P: 0.0004 to 0.01 wt %. Therefore, the saturation magnetic flux density Bs is 440 mT or more, and DC pre-magnetization is excellent. Thus, the present NiMnZn based ferrite material can be used in broad temperature ranges.
In NiMnZn based ferrite, the main components range within the scopes of Fe2O3=53 to 59 mol %, MnO=22 to 39 mol %, ZnO=4 to 12 mol %, and NiO=4 to 7 mol %, and the sub-components of said NiMnZn based ferrite range within the scopes of SiO2: 0.005 to 0.03 wt %, CaO: 0.008 to 0.17 wt % and P: 0.0004 to 0.01 wt %. Therefore, the characteristic of the saturation magnetic flux density Bs is more improved and DC pre-magnetization is excellent. Thus, the present NiMnZn based ferrite material can be used in broad temperature ranges.
In NiMnZn based ferrite, one or two or more of the following additives are added in predetermined ranges of Nb2O5: 0.005 to 0.03 wt %, Ta2O5: 0.01 to 0.08 wt %, V2O5: 0.01 to 0.1 wt %, ZrO2: 0.005 to 0.03 wt %, Bi2O3: 0.005 to 0.04 wt % and MoO3: 0.005 to 0.04 wt %. Therefore, the saturation magnetic flux density Bs is 450 mT or more, and the DC pre-magnetization is more excellent. Thus, the present NiMnZn based ferrite material is low in the power loss.
In the above NiMnZn based ferrite, the average grain size of the sintered body is 6 to 25 xcexcm. Therefore, the present NiMnZn based ferrite is of the small coercivity Hc, the saturation magnetic flux density Bs of 440 mT or more, and the low power loss.
Further, in the present NiMnZn based ferrite, the saturation magnetic flux density Bs (100xc2x0 C.) of the sintered body is 440 mT or more. Therefore, the DC pre-magnetization is excellent.
In the present NiMnZn based ferrite, the relation between the saturation magnetic flux density Bs (150xc2x0 C.) and the coercivity Hc (150xc2x0 C.) of the B-H loop satisfies the condition of R=(Bsxe2x88x92300)2/Hc, (herein Rxe2x89xa7400). Therefore, the DC pre-magnetization is excellent where a value of R (Rxe2x89xa7400) is a parameter.
For transformers or choke coils, the present NiMnZn based ferrite is used. Therefore, it is possible to produce the transformer or the choke coil having the excellent DC pre-magnetization and applicable to broad temperature ranges.